Positive-displacement machines of a helical construction are known from German Patent Publication DE-C-26 03 462. A compressor designed in accordance with this principle is distinguished by nearly pulse-free conveying of the gaseous work medium, for example consisting of air or an air-fuel mixture. For this reason it could also be advantageously employed, among other things, for charging purposes in internal combustion engines. During the operation of such a compressor, a plurality of approximately sickle-shaped work chambers are enclosed along the positive-displacement chamber between the helically-embodied positive-displacement body and the two circumferential walls of the positive-displacement chamber, which move from the inlet through the positive-displacement chamber to the outlet. In the course of this their volume is increasingly decreased, along with a corresponding increase of the work medium pressure. In this connection, the seal between the work chambers upstream and downstream of the compressor is of decisive importance.
A positive-displacement machine of the previously mentioned type is known from U.S. Pat. No. 3,994,636. To obtain an efficient radial seal between the front faces of the positive-displacement device and the lateral walls of the conveying chamber, it is necessary to provide an effective axial contact between the two elements. For this purpose, the positive-displacement device is provided with a groove on its front face, which forms the seat for a sealing strip inserted therein. This sealing strip consists of a resilient material, capable of gliding, and is of such a size that it can be moved in the groove axially and slightly radially. A force-exerting spring element underlies the sealing strip.
The groove causes a perfect lateral guidance of the sealing strip inserted therein. Positioning of the sealing strip in the longitudinal direction takes place through the ends of the groove cut into the helically-shaped walls. Positioning performed in this manner suffices for the loads exerted during operation on the sealing strip inserted in the housing. The sealing strip is sufficiently "caught". Acceleration forces, which are caused by the circulating movement of the helical machine, act during operation on the sealing strip inserted into the grooves disposed on the front face of the helically-shaped strips. These loads have a circulating effect on the sealing strips, i.e. in respect to the sealing strip, the inertial forces do not act on it in one direction, but circularly in the plane of the sealing strip groove. The reaction forces on the sealing strip change their direction accordingly. The transverse components can be well provided by the lateral walls of the groove; the sealing strip is moved forward and back in the groove by the longitudinal component of the reaction forces, in the course of which the ends of the groove form the stop for the relative movement.
The described reaction forces increase with higher operational rpm, wherein in particular the described longitudinal guidance of the sealing strip, which corresponds to the prior art, no longer suffices for the occurring reaction forces. The longitudinal component, which continuously changes its direction, leads to a back-and-forth movement of the sealing strip in the groove, which may result in increased wear of the sealing strips or of the walls of the groove.